In heat exchange units with tubes as the partitions between the two media concerned in the heat exchange, the ends of the tubes, through which the first of the two media flows, are anchored in tubeplates in a manner producing a seal. These tubeplates form partitions between a middle housing part, through which the second medium flows, and one chamber each for the inlet and outlet of the first medium. In low-pressure heat exchange units, for example condensers and low-pressure preheaters, the ends of the heat exchanger tubes are usually rolled into holes in the said tubeplates.
If a tube/tubeplate joint of this type starts to leak, it is as a rule attempted to eliminate this leak by re-rolling the tube ends. In most cases, this is successful if this leak is the first to occur. On repeated re-rolling, however, it is not always possible to seal the leaking areas, since the tubes can then start to crack due to excessive expansion. In these cases, attempts have hitherto been made to restore leak-tightness by means of a weld running around the inner periphery of the tube, the tube material throughout its wall thickness and the adjacent region of the tubeplate material being fused during the weld. Since, however, it is not possible completely to remove the deposits in the narrow gap between the tube and tubeplate, a perfect weld is also not always possible, so that leaks cannot always be eliminated with certainty in its way.